High-precision etching method

ABSTRACT

An embodiment of the present disclosure provides an etching method, having the following steps: forming a modified layer having a thickness of one or several atom layers on a selected region of a surface of a semiconductor material layer by using a modifier; and removing the modified layer. When a semiconductor is processed, this method achieves precise control over the etching thickness and improves the etching rate at the same time.

REFERENCE TO RELATED APPLICATION

This application claims the priority of Chinese Patent Application201810988644.4, entitled “High-Precision Etching Method,” filed on Aug.28, 2018, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to the technical field ofsemiconductors, and more specifically, in particular to a high-precisionetching method.

BACKGROUND ART

As the requirements for various smart electronic devices are increasing,the requirements for small-size and highly functional semiconductorchips increase therewith. Therefore, the extended large-scalerequirements for transistors are accompanied.

Although relatively small sizes of chips may have been achieved atpresent, problems with the processing precision are still encountered.For example, when a nanowire or a nanosheet is processed, the precisecontrol over an etching process appears to be extremely important.Additionally, the selectivity is also very important for a process offorming a nanowire or a nanosheet by etching. The selectivity means thata target semiconductor material is removed by etching while theremaining semiconductor material is substantially intactly kept.

In the prior art, etching is achieved by providing different selectivityratios. This etching process has an extremely high requirement for theselectivity ratio. However, it is more and more difficult to satisfy therequirements for smart electronic devices, due to the substantialdifference between the selectivity ratios of different materials.

In summary, it is urgent to provide a method capable of improving theetching precision of semiconductor processing so as to at least partlysolve the problems described above.

SUMMARY

In order to solve at least some of the problems described above, anembodiment of the present disclosure provides an etching method.

According to an embodiment of the present disclosure, the etching methodcomprises:

forming a modified layer having a thickness of one or several atomlayers on a selected region of a surface of a semiconductor materiallayer by using a modifier; and

removing the modified layer.

In some embodiments, it further comprises, after removing the modifiedlayer: at least cleaning a surface, from which the modified layer isremoved, by using a second cleaning agent.

In some embodiments, it further comprises: performing the steps offorming a modified layer by using a modifier and removing the modifiedlayer repeatedly until a predetermined thickness of a semiconductormaterial layer is etched in the selected region.

In some embodiments, it further comprises, after forming a modifiedlayer by using a modifier and before removing the modified layer: atleast cleaning a surface, on which the modified layer is formed, byusing a first cleaning agent.

In some embodiments, a process of forming the modified layer and aprocess of removing the modified layer are both isotropic.

In some embodiments, the modifier reacts with the selected region of thesurface of the semiconductor material layer, and an increase rate of athickness of the modified layer formed decreases as a time of a reactionwith the modifier increases at least in a period of time.

In some embodiments, the reaction is self-limited.

In some embodiments, the modifier reacts with the selected region of thesurface of the semiconductor material layer until a thickness of themodified layer having a thickness of one or several atom layers reachesa saturation thickness.

In some embodiments, a modified layer formed by a reaction between oneor several atom layers in the selected region of the surface of thesemiconductor material layer and the modifier prevents a furtherreaction between the selected region of the surface of the semiconductormaterial layer and the modifier.

In some embodiments, etching may be performed with an etching precisionof 0.5 nm or less.

In some embodiments, the semiconductor material layer comprises Si orSiGe.

In some embodiments, a rate at which a modified layer formed on a SiGesurface is removed is greater than a rate at which a modified layerformed on a Si surface is removed.

In some embodiments, the modified layer comprises an oxide of Si orSiGe.

In some embodiments, the modifier includes a liquid or aqueous solutioncomprising one or a combination of several of ozone, potassiumpermanganate, potassium dichromate, nitric acid, sulfuric acid, andhydroperoxide, as well as an oxygen-containing gas or anoxygen-containing plasma.

In some embodiments, the etching agent comprises hydrofluoric acid,buffered hydrofluoric acid, BOE, hydrofluoric acid vapor, halogenhydride or vapor thereof, and the like.

In some embodiments, the first cleaning agent and second cleaning agenteach comprise water, high-purity deionized water, ethanol, acetone,isopropanol, or a liquid of a combination of several thereof, or argon,helium, nitrogen, hydrogen, water vapor, or a gas of a combination ofseveral thereof.

In some embodiments, the first cleaning agent and second cleaning agenteach comprise a mixture of water, high-purity deionized water, ethanol,acetone, isopropanol, or a liquid of a combination of several thereofwith a surfactant and/or a hydrophobic coating additive.

In some embodiments, the surfactant comprises an organic matter, whichis an alcohol, an aldehyde, an ester, or an amine, or comprises ahydrophilic group on one end and a hydrophobic group on the other end.

In some embodiments, the hydrophobic coating additive comprisestrimethylchlorosilane, (CH3)₃SiN(CH3)₂, propyldimethylchlorosilane,alkyltrialkoxysilane, hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, and a organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or R^(a) is an aromatic group separated from a silicon atomat a distance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1, 2.

In some embodiments, the hydrolyzable group comprises a halogen or analkoxy group.

In some embodiments, the hydrophilic group on the one end comprises a—OH group or a —COOH group, and the hydrophobic group on the endcomprises a hydrocarbyl group.

According to technical solutions of embodiments of the presentdisclosure, by cyclically performing operations of forming a modifiedlayer and removing the modified layer, precise control (≤0.5 nm) overthe etching thickness is achieved when a semiconductor is processes andthe etching rate is improved at the same time.

DESCRIPTION OF DRAWINGS

The above and other features of the present disclosure will become moreapparent through detailed descriptions hereinbelow in conjunction withaccompanying drawings, in which:

FIG. 1 shows a flow chart of an etching method according to anembodiment of this disclosure;

FIG. 2 shows a flow chart of an etching method according to anotherembodiment of this disclosure;

FIG. 3 shows a flow chart of an etching method according to stillanother embodiment of this disclosure;

FIGS. 4A to 4E show an example of a process of an etching methodaccording to an embodiment of this disclosure;

FIGS. 5A to 5E show another example of a process of an etching methodaccording to an embodiment of this disclosure.

In the accompanying drawings, the same or similar structures arerepresented by the same or similar reference numerals.

DESCRIPTION OF EMBODIMENTS

In order to enable objects, technical solutions, and advantages of thepresent application to be more obvious and clear, detailed descriptionsare further made to the present application in conjunction withaccompanying drawings below. It is to be noted that the followingdescriptions are only for the purpose of illustration, rather thanlimitation to this disclosure. In the description below, numerousspecific details are set forth in order to provide a thoroughunderstanding of this disclosure. However, it is apparent for those ofordinary skill in the art that it is not necessary to implement thisdisclosure by using these specific details. In other examples,well-known circuits, material, or methods are not specifically describedin order to prevent this disclosure from being confused.

Throughout the description, references to “an embodiment”,“embodiments”, “an example”, or “examples”, or “some examples” mean thatspecific features, structures, or characteristics described inconjunction with the embodiment(s) or example(s) are included in atleast one embodiment of this disclosure. Therefore, phrases “in anembodiment”, “in embodiments”, “an example”, or “examples” present invarious positions throughout the description are not necessarily referto the same embodiment or example. Additionally, specific features,structures, or characteristics may be combined one or more embodimentsor examples in any appropriate combination and/or sub-combination.Additionally, it is to be understood by those of ordinary skill in theart that the accompanying drawings provided herein are all for thepurpose of illustration, and the accompanying drawings are notnecessarily drawn to scale. The term “and/or” used herein includes anyand all combinations of one or more of the associated listed items.

FIG. 1 shows a flow chart of an etching method according to anembodiment of this disclosure. As shown in FIG. 1, the etching methodcomprises the steps of:

In step S110, forming a modified layer having a thickness of one orseveral atom layers on a selected region of a surface of a semiconductormaterial layer by using a modifier.

Particularly, the semiconductor material layer to be etched may comprisevarious material layers formed on a substrate. The selected region onthe surface of the semiconductor material layer may comprise a specificregion which is to be processed to form a plurality of features. In aparticular embodiment, the selected region may be processed (forexample, etched) to form a planar region having a certain thickness. Inanother particular embodiment, the selected region may be processed (forexample, etched) to form a region having a groove structure or a viahole structure. However, embodiments of the present disclosure are notlimited thereto.

In an embodiment of the present disclosure, the modifier reacts with thesurface of the semiconductor material layer to be etched to performmodification treatment on the semiconductor, so as to form a modifiedlayer having a thickness of only one or several atom layers on thesurface of the semiconductor material layer.

In a particular embodiment, the specific process of forming the modifiedlayer on the selected region of the surface of the semiconductormaterial layer by using the modifier may comprise allowing the selectedregion of the surface of the semiconductor material layer to react withthe modifier so as to form the modified layer on the selected region ofthe surface of the semiconductor material layer.

In a particular embodiment, in the process in which the modifier reactswith the selected region of the surface of the semiconductor materiallayer, the increase rate of the thickness of the modified layer formeddecreases as the time of the reaction with the modifier increases atleast in a period of time.

In a particular embodiment, the reaction between the modifier and theselected region of the surface of the semiconductor material layerself-limited and the reaction does not stop until the thickness of themodified layer formed having a thickness of one or several atom layersreaches a saturation thickness.

In a particular embodiment, in the process in which the modifier reactswith the selected region of the surface of the semiconductor materiallayer, the modified layer formed covers the surface of the semiconductormaterial layer and can prevent a further reaction between the selectedregion of the surface of the semiconductor material layer and themodifier.

Additionally, in a specific embodiment, the process of forming themodified layer is isotropic. That is, the reaction between the surfaceof the semiconductor material layer and the modifier uniformly occurs inevery direction in which the surface of the semiconductor material layeris in contact with the modifier.

Furthermore, in a specific embodiment, the modifier used may be a liquidor aqueous solution comprising one or a combination of several of ozone(O₃), potassium permanganate (KMnO₄), potassium dichromate (K₂Cr₂O₇),nitric acid (HNO₃), sulfuric acid (H₂SO₄), and hydroperoxide (H₂O₂), ormay be an oxygen-containing gas, an oxygen-containing plasma, or thelike.

Next, in step S120, the modified layer is removed.

Particularly, the modified layer formed may be removed by a method ofetching.

In a particular embodiment, the specific process of removing themodified layer comprises allowing the modified layer formed on thesurface of the semiconductor material layer to be brought into completecontact with an etching agent and performing a reaction between themodified layer and the etching agent to remove the modified layer,wherein the reaction between the modified layer and the etching agent isfinished when the modified layer is completely removed.

As can be seen from the process described above, the process of removingthe modified layer is also somewhat self-limited. That is, when thereaction between the etching agent and the modified layer formed on thesurface of the semiconductor material layer is complete, the process ofetching automatically stops. That is, etching agent will not react witha surface of the semiconductor material layer which is not subjected toa modification reaction.

Additionally, in a specific embodiment, the process of removing themodified layer, i.e., the process of etching described above, isisotropic. That is, the reaction between the modified layer formed onthe surface of the semiconductor material layer and the etching agentuniformly occurs in every direction.

Furthermore, in a specific embodiment, the etching agent used compriseshydrofluoric acid (HF), buffered hydrofluoric acid (BHF), BOE,hydrofluoric acid vapor, halogen hydride or vapor thereof, and the like.wherein BOE is also a buffered etching liquid, which may be formed bymixing HF and NH₄F at various proportions.

In the prior art, a one-step oxidation method is typically used. Sinceit has a high oxidation rate, the thickness of the modified layer formedwill not be conveniently controlled. If oxidation is additionallycontrolled by a special means to be performed slowly, the etching ratewill be overall influenced, leading to an excessively low etching rate.In the present application, the reaction rate is high in the initialphase of the reaction occurring between the surface of the semiconductormaterial layer and the modifier. Since the increase rate of thethickness of the modified layer formed decreases as the time of thereaction with the modifier increases, the reaction rate will rapidlydecrease as the reaction is performed. Therefore, the etching method inan embodiment of the present disclosure can significantly improve theetching rate under the condition where the etching amount or thethickness is well controlled.

One reason is that the thickness of the modified layer formed is athickness of only one or several atom layers. Another reason is that thereaction between the surface of the semiconductor material layer and themodifier automatically stops after the thickness of the modified layerformed on the surface of the semiconductor material layer reaches asaturation thickness. Therefore, the etching method of in an embodimentof the present disclosure can well control the etching thickness andcontributes to more precise control over the etching precision at thesame time.

According to a method in an embodiment of the present disclosure, thesurface of the semiconductor material layer can be etched with anetching precision of 0.5 nm or less or an etching precision superior to0.5 nm.

FIG. 2 shows a flow chart of an etching method according to anotherembodiment of this disclosure. The main differences between thisembodiment and the etching method as shown in FIG. 1 are as follows.

On the one hand, step S215 is performed after forming a modified layerand before removing the modified layer formed (between step S210 andstep S220).

Step S215 comprises at least cleaning a surface, on which the modifiedlayer is formed, by using a first cleaning agent.

After the operation of forming the modified layer is finished, amodifier residue and/or various residues of resultants in the reactionwill be present on the modified layer and/or the surface of thesemiconductor material layer. Therefore, after the operation of formingthe modified layer is finished, it is required to clean the modifiedlayer formed by using a cleaning agent or a surface of the semiconductormaterial layer except the modified layer may be cleaned at the sametime, so as to remove these contaminants, reduce cross contaminationbetween various preceding and succeeding steps, and ensure theprocessing quality of the surface of the semiconductor material layer,and the like.

On the other hand, step S230 is performed after removing the modifiedlayer (after step S220).

Step S230 comprises at least cleaning a surface, from which the modifiedlayer is removed, by using a second cleaning agent.

Likewise, after the operations of forming the modified layer andremoving the modified layer are sequentially finished, a modifierresidue, an etching agent residue, and/or various residues of resultantsin the reaction will be present on the surface of the semiconductormaterial layer. Therefore, after the operations of forming the modifiedlayer and removing the modified layer are sequentially finished, it isrequired to clean the surface of the semiconductor material layer byusing a cleaning agent, so as to remove these contaminants and ensurethe processing quality of the surface of the semiconductor materiallayer.

In a particular embodiment, the first cleaning agent and second cleaningagent used may each comprise water, high-purity deionized water,ethanol, acetone, isopropanol, or a liquid of a combination of severalthereof, or argon, helium, nitrogen, hydrogen, water vapor, or a gas ofa combination of several thereof, or the like.

In a particular embodiment, the first cleaning agent and second cleaningagent used may also each comprise a mixture of water, high-puritydeionized water, ethanol, acetone, isopropanol, a liquid of acombination of several thereof, or the like with a surfactant and/or ahydrophobic coating additive.

The surfactant may reduce the surface tension of the cleaning agent(water, high-purity deionized water, ethanol, acetone, isopropanol, orthe like), and the hydrophobic coating additive may reduce the affinitybetween the cleaning agent (water, high-purity deionized water, ethanol,acetone, isopropanol, or the like) and the surface to be cleaned or mayobtain a surface hydrophobicity. The surfactant and/or hydrophobiccoating additive may be added to the cleaning agent (water, high-puritydeionized water, ethanol, acetone, isopropanol, or the like). In aparticular embodiment, the surfactant used may comprise an organicmatter, which is an alcohol, an aldehyde, an ester, or an amine, orcomprises a hydrophilic group on one end and a hydrophobic group on theother end. Particularly, the hydrophilic group on the one end maycomprise a —OH group or a —COOH group, and the hydrophobic group on theother end may comprise a hydrocarbyl group. The hydrophobic coatingadditive may comprise trimethylchlorosilane (TMCS), TMSDMA((CH3)₃SiN(CH3)₂), propyldimethylchlorosilane, alkyltrialkoxysilane,hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, and a organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or R^(a) is an aromatic group separated from a silicon atomat a distance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1, 2. Thehydrolyzable group comprises a halogen or an alkoxy group. When a solidsurface is treated, one end of the coupling agent reacts with a surfaceactive group and the other end forms a directionally arrangedmonomolecular layer toward air, and there is a significantwater-repelling effect. The hydrophobic coating additive may performsurface treatment or silanization treatment on the surface to becleaned, and the hydrophobic coating additive comprises a silane agent.

Step S210 and step S220 may be performed with reference to step S110 andstep S120 as shown in FIG. 1, and verbose words are omitted herein.

FIG. 3 shows a flow chart of an etching method according to stillanother embodiment of this disclosure.

Step S310, step S315, step S320, and step S330 as shown in FIG. 3 maycorrespond to step S210, step S215, step S220, and step S230 of theembodiment in FIG. 2, respectively. Therefore, the process of performingthese steps may be obtained with reference to the embodiment as shown inFIG. 2, and only differences therein are described herein.

In this embodiment, after step S310, step S315, step S320, and step S330are performed sequentially, it further comprises:

Step S340 of determining whether a predetermined thickness of asemiconductor material layer has been etched in the selected region.That is, whether a predetermined etching amount or etching thickness isreached after one or more processes of forming a modified layer andremoving the modified layer.

If it is determined that a predetermined thickness of a semiconductormaterial layer has been etched in the selected region, the process canbe finished.

If it is determined that a predetermined thickness of a semiconductormaterial layer has not been etched in the selected region, return tostep S310 and perform a cyclic etching process until it is finallydetermined that a predetermined thickness of a semiconductor materiallayer has been etched in the selected region.

In another embodiment of the present disclosure, after a cyclic etchingprocess is finished, the etching amount may be preliminarily estimated,and the thickness is examined only when it is preliminarily estimatedthat a predetermined thickness is reached rather than examined aftereach cyclic etching.

Additionally, in this embodiment, after forming a modified layer byusing a modifier and before removing the modified layer formed, i.e.,between step S310 and step S320, it is required to perform:

Step S315: at least cleaning a surface, on which the modified layer isformed, by using a first cleaning agent.

This is because the modifier and/or the etching agent are typicallyrepeatedly used in the process of cyclic etching for the purpose ofsaving the modifier and/or the etching agent. Therefore, after forming amodified layer, the surface of the modified layer formed is cleaned byusing a first cleaning agent (i.e., step S315 is performed), or thesurface of the semiconductor material layer except the modified layermay be cleaned at the same time, so that the modifier can be preventedfrom being carried by the semiconductor material into the etching agentfor removing the modified layer.

Likewise, in the process of cyclic etching, after removing the modifiedlayer, the surface of the semiconductor material layer exposed again iscleaned by using a second cleaning agent (i.e., step S330 is performed),so that the etching agent for removing the modified layer carried by thesemiconductor material into the repeatedly used modifier may be reduced.

By adding step S315 and step S330, it possible to effectively preventcross contamination in the process of semiconductor etching, prevent theprocess fluctuation, and improve the processing quality.

In a particular embodiment, the first cleaning agent and second cleaningagent used may each comprise water, high-purity deionized water,ethanol, acetone, or isopropanol.

In a particular embodiment, the first cleaning agent and second cleaningagent used may also each comprise a mixture of water, high-puritydeionized water, ethanol, acetone, isopropanol, a liquid of acombination of several thereof, or the like with a surfactant and/or ahydrophobic coating additive.

The surfactant may reduce the surface tension of the cleaning agent(water, high-purity deionized water, ethanol, acetone, isopropanol, aliquid of a combination of several thereof, or the like), and thehydrophobic coating additive may reduce the affinity between thecleaning agent (water, high-purity deionized water, ethanol, acetone,isopropanol, a liquid of a combination of several thereof, or the like)and the surface to be cleaned or may obtain a surface hydrophobicity.The surfactant and/or hydrophobic coating additive may be added to thecleaning agent (water, high-purity deionized water, ethanol, acetone,isopropanol, a liquid of a combination of several thereof, or the like).In a particular embodiment, the surfactant used may comprise an organicmatter, which is an alcohol, an aldehyde, an ester, or an amine, orcomprises a hydrophilic group on one end and a hydrophobic group on theother end. Particularly, the hydrophilic group on the one end maycomprise a —OH group or a —COOH group, and the hydrophobic group on theother end may comprise a hydrocarbyl group. The hydrophobic coatingadditive may comprise trimethylchlorosilane (TMCS), TMSDMA((CH3)₃SiN(CH3)₂), dimethyldichlorosilane, propyldimethylchlorosilane,alkyltrialkoxysilane, hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, and a organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or an aromatic group separated from a silicon atom at adistance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1, 2. thehydrolyzable group comprises a halogen or an alkoxy group. When a solidsurface is treated, one end of the coupling agent reacts with a surfaceactive group and the other end forms a directionally arrangedmonomolecular layer toward air, and there is a significantwater-repelling effect. The hydrophobic coating additive may performsurface treatment or silanization treatment on the surface to becleaned, and the hydrophobic coating additive comprises a silane agent.

According to technical solutions of embodiments of the presentdisclosure, the precise control over the etching thickness when asemiconductor is processes is achieved by cyclically performingoperations of forming a modified layer and removing the modified layer.

The etching method of the present disclosure and the etching effectthereof will be described in more detail below in conjunction withspecific examples according to embodiments of the present disclosure asshown in FIGS. 4A to 4E and FIGS. 5A to 5E.

With reference to FIGS. 4A to 4E, an example of a process of an etchingmethod according to an embodiment of this disclosure is shown. Moreparticularly, FIGS. 4A to 4E show an example in which a surface of asemiconductor material layer to be etched is an exposed Si surface orSiGe surface.

As shown in FIG. 4A, a substrate having an exposed patterned Si surface(or SiGe surface) 41 is first provided. Additionally, the upper side ofthe Si surface (or SiGe surface) 41 is further covered with a nitridelayer 42.

Next, as shown in FIG. 4B, the substrate described above is placed inits entirety into a surface modifier 43. The modifier 43 used may be aliquid or aqueous solution comprising one or a combination of several ofozone (O₃), potassium permanganate (KMnO₄), potassium dichromate(K₂Cr₂O₇), nitric acid (HNO₃), sulfuric acid (H₂SO₄), and hydroperoxide(H₂O₂), or may be an oxygen-containing gas, an oxygen-containing plasma,or the like.

Since the surface of Si (or SiGe) except the uppermost surface coveredby the nitride layer 42 is completely in contact with the modifier 43,the surface described above reacts with the modifier 43 to consume acertain amount of Si (or SiGe) and form a thin modified layer 40 on thesurface. For example, the modified layer may be specifically an oxide ofSi (or SiGe) having a thickness of one or several atom layers.

Since the uppermost surface of Si (or SiGe) is covered by the nitridelayer 42, it is prevented from being brought into contact with themodifier 43. Therefore, the modified layer 40 will not be formed on theuppermost surface of Si (or SiGe).

When the thickness of the modified layer formed on the exposed surfaceof Si (or SiGe) reaches a saturation thickness, the reaction between theexposed surface of Si (or SiGe) and the modifier 43 is finished.

Next, it is desired to clean the reacted surface by using a firstcleaning agent.

Preferably, the surface of the modified layer formed may be cleaned byusing a cleaning agent such as water, high-purity deionized water,acetone, or a liquid of a combination of several thereof, or argon,helium, nitrogen, hydrogen, water vapor, or a gas of a combination ofseveral thereof, or the like. In this way, the residue of the modifiermay be prevented, as shown in FIG. 4C. Preferably, in order to reducethe surface tension of the cleaning agent (water, high-purity deionizedwater, ethanol, acetone, isopropanol, a liquid of a combination ofseveral thereof, or the like) and/or the affinity between the cleaningagent and the surface to be cleaned, the surfactant and/or hydrophobiccoating additive may also be added to the cleaning agent (water,high-purity deionized water, ethanol, acetone, isopropanol, or a liquidof a combination of several thereof) to clean the surface of themodified layer formed. The surfactant used may comprise an organicmatter, which is an alcohol, an aldehyde, an ester, or an amine, orcomprises a hydrophilic group on one end and a hydrophobic group on theother end. Particularly, the hydrophilic group on the one end maycomprise a —OH group or a —COOH group, and the hydrophobic group on theother end may comprise a hydrocarbyl group. The hydrophobic coatingadditive may reduce the affinity between the cleaning agent (water,high-purity deionized water, ethanol, acetone, isopropanol, or a liquidof a combination of several thereof) and the surface to be cleaned ormay obtain a surface hydrophobicity. The surfactant and/or hydrophobiccoating additive may be added to the cleaning agent (water, high-puritydeionized water, ethanol, acetone, isopropanol, or a liquid of acombination of several thereof). In a particular embodiment, thesurfactant used may comprise an organic matter, which is an alcohol, analdehyde, an ester, or an amine, or comprises a hydrophilic group on oneend and a hydrophobic group on the other end. Particularly, thehydrophilic group on the one end may comprise a —OH group or a —COOHgroup, and the hydrophobic group on the other end may comprise ahydrocarbyl group. The hydrophobic coating additive may comprisetrimethylchlorosilane (TMCS), TMSDMA ((CH3)₃SiN(CH3)₂),dimethyldichlorosilane, propyldimethylchlorosilane,alkyltrialkoxysilane, hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, and a organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or R^(a) is an aromatic group separated from a silicon atomat a distance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1, 2. Thehydrolyzable group comprises a halogen or an alkoxy group. When a solidsurface is treated, one end of the coupling agent reacts with a surfaceactive group and the other end forms a directionally arrangedmonomolecular layer toward air, and there is a significantwater-repelling effect. The hydrophobic coating additive may performsurface treatment or silanization treatment on the surface to becleaned, and the hydrophobic coating additive comprises a silane agent.

Then, Si (or SiGe), which is cleaned and formed with the modified layer40, is etched by using an etching agent to remove the modified layer 40.The etching agent used may be hydrofluoric acid (HF), bufferedhydrofluoric acid (BHF), BOE, hydrofluoric acid vapor, halogen hydrideor vapor thereof, and the like. After etching is finished, the surfaceof Si (or SiGe), which is originally exposed, is etched off and reducedor is partly etched, while the uppermost surface of Si (or SiGe) coveredwith the nitride layer 42 is not etched, as shown in FIG. 4D.

Preferably, after the process of etching is finished, the surface of thesemiconductor material layer is cleaned by using a second cleaning agentto remove an etching agent residue and/or various residues of resultantsin the reaction so as to prevent cross contamination. Preferably, thesurface of the semiconductor may be cleaned by using water, high-puritydeionized water, ethanol, acetone, isopropanol, or a liquid of acombination of several thereof, or argon, helium, nitrogen, hydrogen,water vapor, or a gas of a combination of several thereof, or the like.Preferably, in order to reduce the surface tension of the cleaning agent(water, high-purity deionized water, ethanol, acetone, isopropanol, or aliquid of a combination of several thereof), and since the hydrophobiccoating additive may reduce the affinity between the cleaning agent(water, high-purity deionized water, ethanol, acetone, isopropanol, or aliquid of a combination of several thereof) and the surface to becleaned or may obtain a surface hydrophobicity, the surfactant may alsobe added to the cleaning agent to clean the surface of thesemiconductor. The surfactant used may comprise an organic matter, whichis an alcohol, an aldehyde, an ester, or an amine, or comprises ahydrophilic group on one end and a hydrophobic group on the other end.Particularly, the hydrophilic group on the one end may comprise a —OHgroup or a —COOH group, and the hydrophobic group on the other end maycomprise a hydrocarbyl group. The hydrophobic coating additive mayreduce the affinity between the cleaning agent (water, high-puritydeionized water, ethanol, acetone, isopropanol, a liquid of acombination of several thereof, or the like) and the surface to becleaned or may obtain a surface hydrophobicity. The surfactant and/orhydrophobic coating additive may be added to the cleaning agent (water,high-purity deionized water, ethanol, acetone, isopropanol, a liquid ofa combination of several thereof, or the like). In a particularembodiment, the surfactant used may comprise an organic matter, which isan alcohol, an aldehyde, an ester, or an amine, or comprises ahydrophilic group on one end and a hydrophobic group on the other end.Particularly, the hydrophilic group on the one end may comprise a —OHgroup or a —COOH group, and the hydrophobic group on the other end maycomprise a hydrocarbyl group. The hydrophobic coating additive maycomprise trimethylchlorosilane (TMCS), TMSDMA ((CH3)₃SiN(CH3)₂),dimethyldichlorosilane, propyldimethylchlorosilane,alkyltrialkoxysilane, hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, and a organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or R^(a) is an aromatic group separated from a silicon atomat a distance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1, 2. Thehydrolyzable group comprises a halogen or an alkoxy group. When a solidsurface is treated, one end of the coupling agent reacts with a surfaceactive group and the other end forms a directionally arrangedmonomolecular layer toward air, and there is a significantwater-repelling effect. The hydrophobic coating additive may performsurface treatment or silanization treatment on the surface to becleaned, and the hydrophobic coating additive comprises a silane agent.

Finally, whether the exposed surface of Si (or SiGe) has been alreadyetched to a predetermined thickness is determined. If not, operations offorming a modified layer and removing the modified layer are repeatedlyperformed with reference to FIGS. 4B to 4D, until a predeterminedetching thickness is reached as shown in FIG. 4E.

As can be seen, in this example, selective etching of a part of thesurface of Si (or SiGe), i.e., the exposed surface of Si (or SiGe), isachieved by forming the modified layer several times and etching themodified layer several times.

With reference to FIGS. 5A to 5E, another example of a process of anetching method according to an embodiment of this disclosure is shown.More particularly, FIGS. 5A to 5E show an example in which a surface ofa semiconductor material layer to be processed is a partial surface(exposed surface) having a SiGe layer.

As shown in FIG. 5A, First, exposed patterned Si layer 51, SiGe layer52, and Si layer 53 are formed on a Si substrate. The SiGe layer 52 andthe Si layer 53 may be generated by deposition and subsequent patterningby using a method such as epitaxial growth, CVD, or the like. As can beseen from the figure, the semiconductor structure has both a Si surfaceand a SiGe surface, which are exposed.

Next, the substrate described above is placed in its entirety into asurface modifier 54. The modifier 54 used may be a liquid or aqueoussolution comprising one or a combination of several of ozone (O₃),potassium permanganate (KMnO₄), potassium dichromate (K₂Cr₂O₇), nitricacid (HNO₃), sulfuric acid (H₂SO₄), and hydroperoxide (H₂O₂), or may bean oxygen-containing gas, an oxygen-containing plasma, or the like, asshown in FIG. 5B.

A modified layer 50 will be formed on both the Si surface and the SiGesurface, which are exposed, due to the effect of the modifier. Themodified layer 50 may be specifically an oxide of Si or an oxide of SiGe(for example, SiGeO) having a thickness of one or several atom layers.

Next, it may be optional to clean the reacted surface by using a firstcleaning agent.

Preferably, the surface of the modified layer formed may be cleaned byusing a cleaning agent such as water, high-purity deionized water,ethanol, acetone, isopropanol, or a liquid of a combination of severalthereof, or argon, helium, nitrogen, hydrogen, water vapor, or a gas ofa combination of several thereof, or the like. In this way, the residueof the modifier may be prevented, as shown in FIG. 5C. Preferably, afirst cleaning agent (water, high-purity deionized water, ethanol,acetone, isopropanol, a liquid of a combination of several thereof, orthe like) comprising a surfactant and/or a hydrophobic coating additivemay also be used to at least clean the surface of the modified layerformed. The surfactant used may reduce the surface tension of the firstcleaning agent (water, high-purity deionized water, ethanol, acetone,isopropanol, or a liquid of a combination of several thereof) and/or theaffinity between the first cleaning agent and the surface of themodified layer. The surfactant used may comprise an organic matter,which is an alcohol, an aldehyde, an ester, or an amine, or comprises ahydrophilic group on one end and a hydrophobic group on the other end.Particularly, the hydrophilic group on the one end may comprise a —OHgroup or a —COOH group, and the hydrophobic group on the other end maycomprise a hydrocarbyl group. The hydrophobic coating additive mayreduce the affinity between the cleaning agent (water, high-puritydeionized water, ethanol, acetone, isopropanol, a liquid of acombination of several thereof, or the like) and the surface to becleaned or may obtain a surface hydrophobicity. The surfactant and/orhydrophobic coating additive may be added to the cleaning agent (water,high-purity deionized water, ethanol, acetone, isopropanol, a liquid ofa combination of several thereof, or the like). In a particularembodiment, the surfactant used may comprise an organic matter, which isan alcohol, an aldehyde, an ester, or an amine, or comprises ahydrophilic group on one end and a hydrophobic group on the other end.Particularly, the hydrophilic group on the one end may comprise a —OHgroup or a —COOH group, and the hydrophobic group on the other end maycomprise a hydrocarbyl group. The hydrophobic coating additive maycomprise trimethylchlorosilane (TMCS), TMSDMA ((CH3)₃SiN(CH3)₂),dimethyldichlorosilane, propyldimethylchlorosilane,alkyltrialkoxysilane, hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, and a organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or R^(a) is an aromatic group separated from a silicon atomat a distance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1, 2. Thehydrolyzable group comprises a halogen or an alkoxy group. When a solidsurface is treated, one end of the coupling agent reacts with a surfaceactive group and the other end forms a directionally arrangedmonomolecular layer toward air, and there is a significantwater-repelling effect. The hydrophobic coating additive may performsurface treatment or silanization treatment on the surface to becleaned, and the hydrophobic coating additive comprises a silane agent.

Then, the modified layer 50 is etched by using an etching agent toremove the modified layer 50. The etching agent used may be hydrofluoricacid (HF), buffered hydrofluoric acid (BHF), BOE, hydrofluoric acidvapor, halogen hydride or vapor thereof, and the like.

It is to be noted that selective etching of SiGe can be achieved in thisexample, as shown in FIGS. 5D and 5E. Little or only a small amount ofthe Si surface, which is originally exposed, is etched off, so as toexpose its surface. A certain thickness of the exposed surface of SiGeis remarkably reduced due to a high etching rate.

In the phase of forming the modified layer, a specific modifier and anappropriate process control (for example, a reaction temperature of 5 Cto 90 C and/or a reaction time of 1 second to 200 seconds) are used, sothat the forming rate of the modified layer on the SiGe surface may begreater than the forming rate of the modified layer on the Si surface.Therefore, the thickness of the modified layer formed on the SiGesurface will be greater than the thickness of the modified layer formedon the Si surface within the same reaction time. In other words, thenumber of atoms of Si and Ge consumed in forming the modified layer onthe SiGe surface is greater than the number of atoms of Si consumed onthe Si surface. Thus, after the modified layer formed is etched, theSiGe layer 52 will be etched more while the Si layer 51 and the Si layer53 will be etched less, as shown in FIGS. 5D and 5E. Therefore,selective etching of SiGe is achieved.

More particularly, the increase rate of the thickness of the modifiedlayer increases as the temperature of the modifier increases, andincreases as the concentrations of ozone (O₃), potassium permanganate(KMnO₄), potassium dichromate (K₂Cr₂O₇), nitric acid (HNO₃), sulfuricacid (H₂SO₄), and hydroperoxide (H₂O₂) contained in the modifierincrease. It is also possible to increase the reaction rate or increasethe growth rate of the modified layer by stirring the modifier.

In another aspect, in the phase of forming the modified layer, althoughthere may be a problem of different rates at which the modified layer ofthe SiGe surface and the modified layer of the Si surface are formed,selective etching of SiGe may be optionally achieved in the process ofremoving the modified layer if the difference in the thicknesses of themodified layers formed is not very large.

Particularly, in the phase of etching the modified layer, a specificetching agent and an appropriate process control (for example, anetching temperature of 5 C to 80 C and/or an etching time of 2 secondsto 120 seconds) are used, so that the etching rate of the modified layerformed on the SiGe surface is greater than the etching rate of themodified layer formed on the Si surface. Therefore, when the etching ofthe modified layer formed on the SiGe surface is finished to expose theSiGe surface again, the modified layer formed on the Si surface may havenot been already etched. In another example, only a small part or noneof the modified layer formed on the Si surface may be etched off. Thus,the modified layer formed on the Si surface may be used as a protectivelayer structure, which protects the Si surface in subsequent cyclicetching processes. SiGe is then gradually etched by subsequent cyclicetching processes and selective etching of SiGe is finally achieved.

Unlike the selective etching achieved mainly on the basis of the phaseof removing the modified layer, the selective etching achieved on thebasis of the phase of forming the modified layer requires a material tobe selectively etched (for example, SiGe), wherein the thickness of themodified layer formed therefrom or the consumption amount of thematerial to be selectively etched must be greater than the thickness ofthe modified layer formed from the material which is not selectivelyetched (for example, Si) or the consumption amount thereof, as shown inFIGS. 5B and 5C. The selective etching achieved on the basis of thephase of removing the modified layer does not require the differencebetween the thicknesses of the modified layers formed from the twomaterials.

Additionally, different etching rates of SiGe and Si may be achieved byadjusting the content of Ge in SiGe. Therefore, the content of Ge inSiGe is preferably greater than 10% (Ge %>10%) in order to obtain a goodetching selectivity, when SiGe is etched at a rate higher than the rateat which Si is etched.

In this example, it is also determined whether the exposed surface ofSiGe has been already etched to a predetermined thickness. If thepredetermined thickness is not reached, the predetermined etchingthickness is achieved by cyclic etching. Next, it may be optional toclean the reacted surface by using a second cleaning agent. Preferably,the surface of the modified layer formed may be cleaned by using acleaning agent such as water, high-purity deionized water, ethanol,acetone, isopropanol, or a liquid of a combination of several thereof,or argon, helium, nitrogen, hydrogen, water vapor, or a gas of acombination of several thereof, or the like. Preferably, a secondcleaning agent (water, high-purity deionized water, ethanol, acetone,isopropanol, or a liquid of a combination of several thereof) comprisinga surfactant and/or a hydrophobic coating additive may also be used toat least clean the surface of the modified layer formed. The surfactantused may reduce the surface tension of the second cleaning agent (water,high-purity deionized water, ethanol, acetone, isopropanol, or a liquidof a combination of several thereof) and/or the affinity between thecleaning agent and the surface of Si or SiGe. The surfactant comprisesan organic matter, which is an alcohol, an aldehyde, an ester, or anamine, or comprises a hydrophilic group on one end and a hydrophobicgroup on the other end. Particularly, the hydrophilic group on the oneend may comprise a —OH group or a —COOH group, and the hydrophobic groupon the other end may comprise a hydrocarbyl group. The hydrophobiccoating additive may reduce the affinity between the cleaning agent(water, high-purity deionized water, ethanol, acetone, isopropanol, aliquid of a combination of several thereof, or the like) and the surfaceto be cleaned or may obtain a surface hydrophobicity. The surfactantand/or hydrophobic coating additive may be added to the cleaning agent(water, high-purity deionized water, ethanol, acetone, isopropanol, aliquid of a combination of several thereof, or the like). In aparticular embodiment, the surfactant used may comprise an organicmatter, which is an alcohol, an aldehyde, an ester, or an amine, orcomprises a hydrophilic group on one end and a hydrophobic group on theother end. Particularly, the hydrophilic group on the one end maycomprise a —OH group or a —COOH group, and the hydrophobic group on theother end may comprise a hydrocarbyl group. The hydrophobic coatingadditive may comprise trimethylchlorosilane (TMCS), TMSDMA((CH3)₃SiN(CH3)₂), dimethyldichlorosilane, propyldimethylchlorosilane,alkyltrialkoxysilane, hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, and a organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or R^(a) is an aromatic group separated from a silicon atomat a distance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1, 2. Thehydrolyzable group comprises a halogen or an alkoxy group. When a solidsurface is treated, one end of the coupling agent reacts with a surfaceactive group and the other end forms a directionally arrangedmonomolecular layer toward air, and there is a significantwater-repelling effect. The hydrophobic coating additive may performsurface treatment or silanization treatment on the surface to becleaned, and the hydrophobic coating additive comprises a silane agent.In this way, the residue of the modifier may be prevented, as shown inFIG. 5C. Specifically, operations may be performed with reference toembodiments and specific examples described above, and verbose words areomitted herein.

As can be seen, in this example, selective etching of the SiGe surface,i.e., the exposed SiGe surface, is achieved by forming the modifiedlayer several times and etching the modified layer several times, in thecase where both the Si surface and the SiGe surface are exposed, on thebasis that the rate at which the modified layer is formed on the SiGesurface is greater than the rate at which the modified layer is formedon the Si surface or the rate at which the modified layer formed on theSiGe surface is removed is greater than the rate at which the modifiedlayer formed on the Si surface is removed.

It can be understood by those skilled in the art that the methods asillustrated above are merely exemplary. The method of the presentdisclosure is not limited to the steps and the orders as illustratedabove. Numerous variations and modifications may be made by thoseskilled in the art according to the teachings of the embodimentsillustrated.

Although the present disclosure has been illustrated above inconjunction with preferred embodiments of the present disclosure, itwill be understood by those skilled in the art that variousmodifications, substitutions, and variations may be made to the presentdisclosure without departing from the spirit and the scope of thepresent disclosure. Therefore, the present disclosure should not belimited by the embodiments described above, but should be limited by theappended claims and equivalents thereof.

What is claimed is:
 1. A selective etching method, comprising: a step offorming a modified layer having a thickness of one or several atomlayers on a selected region of a surface of a semiconductor materiallayer by using a modifier, wherein the semiconductor material layercomprises Si as a first solid material and SiGe as a second solidmaterial, the selected region includes an exposed surface of the firstsolid material and an exposed surface of the second solid material, arate of forming the modified layer on the surface of the second solidmaterial is greater than a rate of forming the modified layer on thesurface of the first solid material, so that the modified layer on thesurface of the second solid material has a thickness greater than thatof the modified layer on the surface of the first solid material; and astep of removing the modified layer, wherein the modified layer on thesurface of the first solid material and the modified layer on thesurface of the second solid material are etched simultaneously, untilthe modified layer on the surface of the second solid material isremoved completely.
 2. The method according to claim 1, furthercomprising: after the step of removing the modified layer, at leastcleaning a surface, from which the modified layer is removed, by using asecond cleaning agent, and/or, after the step of forming a modifiedlayer by using a modifier and before the step of removing the modifiedlayer, at least cleaning a surface, on which the modified layer isformed, by using a first cleaning agent.
 3. The method according toclaim 2, wherein the first cleaning agent or second cleaning agentcomprises water, high-purity deionized water, ethanol, acetone,isopropanol, or a liquid of a combination of several thereof, or argon,helium, nitrogen, hydrogen, water vapor, or a gas of a combination ofseveral thereof.
 4. The method according to claim 2, wherein the firstcleaning agent or second cleaning agent comprises a mixture of water,high-purity deionized water, ethanol, acetone, isopropanol, or a liquidof a combination of several thereof with a surfactant and/or ahydrophobic coating additive.
 5. The method according to claim 4,wherein the surfactant comprises an organic matter, which is an alcohol,an aldehyde, an ester, or an amine, or comprises a hydrophilic group onone end and a hydrophobic group on the other end.
 6. The methodaccording to claim 4, wherein the hydrophobic coating additive comprisestrimethylchlorosilane, (CH3)₃SiN(CH3)₂, propyldimethylchlorosilane,alkyltrialkoxysilane, hexadecyltrimethoxysilane, tetraethoxysilane,3-glycidyloxypropyltrimethoxysilane, or an organosilicon coupling agentR^(a)Si(R^(b))_(n)X_(3-n), wherein R^(a) is a C₁₋₂₄ linear or branchedalkyl group or R^(a) is an aromatic group separated from a silicon atomat a distance of 1 to 8 carbon atoms, R^(b) is a C₁₋₆ short linear orbranched alkyl group, X is a hydrolyzable group, and n=0, 1,
 2. 7. Themethod according to claim 6, wherein the hydrolyzable group comprises ahalogen or an alkoxy group.
 8. The method according to claim 5, whereinthe hydrophilic group comprises a —OH group or a —COOH group, and thehydrophobic group comprises a hydrocarbyl group.
 9. The method accordingto claim 1, further comprising: performing the steps of forming amodified layer by using a modifier and removing the modified layerrepeatedly until a predetermined thickness of a semiconductor materiallayer is etched in the selected region.
 10. The method according toclaim 1, wherein a process of forming the modified layer and a processof removing the modified layer are both isotropic.
 11. The methodaccording to claim 1, wherein the modifier reacts with the selectedregion of the surface of the semiconductor material layer, and anincrease rate of a thickness of the modified layer formed decreases as atime of a reaction with the modifier increases at least in a period oftime.
 12. The method according to claim 11, wherein the reaction isself-limited.
 13. The method according to claim 12, wherein the modifierreacts with the selected region of the surface of the semiconductormaterial layer until a thickness of the modified layer having athickness of one or several atom layers reaches a saturation thickness.14. The method according to claim 11, wherein a modified layer formed bya reaction between one or several atom layers in the selected region ofthe surface of the semiconductor material layer and the modifierprevents a further reaction between the selected region of the surfaceof the semiconductor material layer and the modifier.
 15. The methodaccording to claim 1, wherein etching may be performed with an etchingprecision of 0.5 nm or less.
 16. The method according to claim 1,wherein a rate at which a modified layer formed on a SiGe surface isremoved is greater than a rate at which a modified layer formed on a Sisurface is removed, so that a part of the modified layer formed on theSi surface still remains when the modified layer formed on the SiGesurface has been completely removed, and the remained modified layerserves as a protective layer for Si.
 17. The method according to claim1, wherein the modified layer comprises an oxide of Si and an oxide ofSiGe.
 18. The method according to claim 1, wherein the modifier includesa liquid or aqueous solution comprising one or a combination of severalof ozone, potassium permanganate, potassium dichromate, nitric acid,sulfuric acid, and hydroperoxide, as well as an oxygen-containing gas oran oxygen-containing plasma.
 19. The method according to claim 18,wherein the modified layer is removed by an etching agent, wherein theetching agent comprises hydrofluoric acid, buffered hydrofluoric acid, amixture of HF and NH₄F, hydrofluoric acid vapor, halogen hydride orvapor thereof.